JP4368626B2 - Image reading device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image reading apparatus applicable to a facsimile apparatus, a scanner apparatus, a copying machine, a digital multifunction machine, and the like, and in particular, a main scanning direction scan line on a reading surface of a document is a sub scanning direction. A light source that illuminates the scan line on the reading surface over the entire main scanning direction, and photoelectrically converts light emitted from the light source and reflected by the scan line on the reading surface by a line image sensor. The present invention relates to an image reading apparatus for obtaining image data corresponding to the reading surface of the original.
[0002]
[Prior art]
When reading an original in units of main scanning lines in an image reading device, ideally it is sufficient if the reflectance of light in the image area of the main scanning line can be detected, but actually reading is performed by detecting the intensity of reflected light of the irradiated light. Is going.
[0003]
In this case, if the amount of light to be irradiated is uniform in the main scanning line direction, the intensity of the reflected light is ideally equivalent to the reflectance of light in the image area of the main scanning line.
[0004]
However, in reality, a xenon tube or LED array used as a light source cannot emit light with a uniform amount of light in the main scanning direction. Even if it is possible, due to non-uniformity (unevenness) in the attenuation characteristic in the main scanning direction in the reading optical system, the light amount of the light source is uneven in the main scanning direction when it is received by the line image sensor. Equivalent undesirable effects. Some image reading apparatuses using a contact image sensor irradiate light from an LED light source onto a document surface via a light guide plate. However, there is also a problem of unevenness in the light amount distribution in the main scanning direction.
[0005]
In order to cope with such a light source itself or / and unevenness in the light amount distribution in the main scanning direction and attenuation characteristics in the reading optical system, physical measures such as arranging a shading plate can be taken. Not only does this require space, it also increases the equipment cost.
[0006]
Further, it cannot cope with variations in the light emission characteristics of the light source for each apparatus, variations in the attenuation characteristics in the reading optical system, and changes with time of these variations.
[0007]
If the unevenness of the light source in the main scanning direction and / or the reading optical system is not eliminated at the stage of entering the line image sensor, the image signal in the bright area of the unevenness must be processed correctly. In the analog and digital image processing, when the unevenness is corrected by the shading correction processing, there is a problem that the accuracy of the image signal from the dark region is lowered and the image quality is deteriorated.
[0008]
Various improvements such as the proposal described in Patent Document 1 have been made for the light source of the image reading apparatus.
[0009]
[Patent Document 1]
JP-A-5-328025
[0010]
[Problems to be solved by the invention]
However, even with various proposals such as Patent Document 1, it has been impossible to solve the above-mentioned problems of the prior art.
[0011]
The present invention has been made in view of such circumstances, can read a document image with uniform sensitivity in the main scanning direction, can minimize power consumption and heat generation required for document illumination, An object of the present invention is to provide an image reading apparatus capable of maintaining high image quality.
[0012]
[Means for Solving the Problems]
  Of the present inventionThe image reading apparatus moves the scan line in the main scanning direction, which is the current reading position on the reading surface of the document, in the sub-scanning direction,the aboveA light source that illuminates the scan line on the reading surface over the entire main scanning direction is emitted from the light source.the aboveLight reflected from the scan line on the reading surface is photoelectrically converted by the line image sensor.the aboveIn an image reading apparatus for obtaining image data corresponding to a reading surface of a document,the aboveMultiple light source blocksthe aboveWhile configured as a plurality of arrays in the main scanning direction,the aboveFor each light source block, a light source block individual driving means for lighting and driving with a set light amount that is equal to or less than the maximum output light amount, and a white reference plate before starting document reading.the aboveWhite image data obtained by reading with a line image sensorthe aboveThe signal level in the main scanning direction is almost constantthe aboveFor light source block individual drive meansthe aboveLight source block-specific light amount setting means for adaptively setting the light amount of each light source blockThe light amount setting and driving of each light source block are performed by changing the duty ratio, which is the ratio of the light emission period in a predetermined driving cycle. When the light quantity of each light source block is adaptively set by setting the duty ratio so that the signal level in the main scanning direction of the white image data obtained by reading the white reference plate with the line image sensor is substantially constant. When the set value of the duty ratio falls below the predetermined lower limit value, the setting is not made below the lower limit duty ratio, and the maximum and minimum values of the duty ratio set for each of the light source blocks. When the difference from the value exceeds the predetermined upper limit difference, the difference in the set value of the duty ratio for each of the light source blocks is Within a range equal to or less than the serial upper limit difference is obtained so as to set the duty ratio for each of said respective light source blocks.
[0013]
  the aboveConfigure the light sourcethe aboveFor each light source blockthe aboveThe maximum output light intensity isthe aboveSet to an amount that almost cancels the known attenuation characteristics in the main scanning direction in the reading optical system through which reflected light from the scan line of the original passes before entering the image sensor.Good.
[0014]
  the aboveConfigure the light sourcethe aboveFor each light source blockthe aboveThe maximum output light intensity isthe aboveThe reflected light from the scan line of the documentthe aboveWhile it is set to an amount that substantially cancels the known attenuation characteristic that is substantially symmetrical in the main scanning direction in the reading optical system that passes through before entering the image sensor,the aboveThe light source block individual driving means includes the light source blocks.the aboveTwo light source blocks that are substantially symmetrical in the main scanning direction are driven to light as one light source block.Good.
[0015]
  the aboveEach light source block is composed of multiple light emitting diode elements arranged in parallel in the main scanning directionGood.
[0016]
  When performing a predetermined image correction process on the document image data obtained from the line image sensor, each partial image data corresponding to each light source block in the main scanning direction Each is further provided with duty ratio adaptive image correction means for performing correction suitable for each duty ratio set by the light source block-specific light amount setting means.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[0021]
First, FIG. 1 shows the scanner mechanism of the image processing apparatus 1 according to the present embodiment. As the scanner mechanism, there are an equal magnification type using a contact image sensor and a type using a CCD image sensor and a reduction optical system. The image processing apparatus 1 according to the present embodiment is the latter type. Type. However, the present invention is equally possible for the former type.
[0022]
In the figure, a document to be read is placed on the contact glass 50 disposed on the upper surface of the apparatus with the reading surface facing down.
[0023]
The scan line Ls is a line on which the reflected light from the line-shaped partial image region in the main scanning direction at that position on the document is imaged and read on the CCD 60, and in the vicinity centering on the scan line Ls, contact glass The light from the light source unit 52 arranged below 50 is irradiated.
[0024]
The irradiated light is reflected by the line-shaped image region at the position of the scan line Ls on the document, and the reflected light is sequentially reflected by the mirror 53, the mirror 54, and the mirror 55 to constitute a reduction optical system. One main scan incident on the lens 56, imaged on a line-shaped light receiving element group of the CCD 60 disposed on the CCD substrate 70, photoelectrically converted, and corresponding to the line-shaped image region at the position of the scan line Ls on the document Analog image signals for lines are obtained, and the analog image signals are sent to a reading control unit 6 described later via a CCD substrate 70 on which the CCD 60 is mounted.
[0025]
The light source unit 52 and the mirrors 53, 54, and 55 are mounted on a carriage (not shown). The optical positional relationship between the carriage 56 and the lens 56 and the CCD 60 fixed on the main body side by a sub-scanning mechanism (not shown). The scanning line Ls moves in the sub-scanning direction by moving in the sub-scanning direction shown in FIG. Is obtained.
[0026]
Further, when the scan line Ls is moved to the position of the white reference plate 51 disposed at the end of the upper surface of the contact glass 50 and image data for one main scan line is acquired at that position, the image data is white. Non-uniformity in intensity of emitted light in the main scanning direction of the light source unit 52, reflection unevenness in reflection or transmitted light in the main scanning direction in the reading optical system of the mirrors 53, 54, and 55, and It is used for a shading correction process, which is a process for correcting the overall unevenness of the reading system by integrating the unevenness of sensitivity between the light receiving elements arranged in the main scanning direction constituting the CCD 56.
[0027]
Compensation of such unevenness of the reading system is performed by, for example, obtaining the highest signal level 100 from a specific light receiving element in the image data for one main scanning line obtained by reading the uniform white reference plate 51. When the lowest signal level 50 is obtained from another light receiving element, the shading correction is performed so that the image data obtained from the light receiving element having the lowest signal level 50 is doubled. However, if there is too much variation in the image signal level obtained from each light receiving element, the image signal from the light receiving element with a low signal level cannot be used effectively in the analog image processing circuit, There is a problem that sufficient accuracy cannot be obtained at the time of A / D conversion for converting an image signal into digital image data.
[0028]
Therefore, even if unevenness in photoelectric conversion characteristics between the light receiving elements constituting the CCD 60 is unavoidable, correction of unevenness in the reading optical system of the light source unit 52, the mirrors 53, 54, 55, and the lens 56 has been conventionally performed. It was done.
[0029]
Specifically, the lens 56 has a characteristic that the attenuation amount of transmitted light increases from the center toward the edge (both ends of the image data for one main scanning line become dark) according to the COS fourth law. Since it is known in advance, a shading plate that physically adjusts the amount of light from the light source unit 52 to the reading surface of the document is disposed so as to eliminate the characteristic.
[0030]
Although the illustration of the image processing apparatus 1 according to the present embodiment shown in FIG. 1 is also omitted, a shading plate is disposed so as to correct unevenness of the lens 56 for the COS fourth power law.
[0031]
FIG. 2 shows a block configuration of the image forming apparatus 1 according to the present embodiment.
[0032]
In the figure, a CPU 2 is a central processing unit that controls each part of the apparatus and performs various data processing based on a control program written in a ROM 3 while using a RAM 4 as a work area.
[0033]
As described above, the ROM 3 is a read-only memory in which a control program for the CPU 2 to control each part of the apparatus is stored. The RAM 4 is a random access memory used as a work area for the CPU 2 as described above.
[0034]
The parameter memory 5 stores various types of information necessary for the operation of the apparatus and retains the stored contents even when the apparatus is turned off. Specifically, the parameter memory 5 is an EEPROM (electrically rewritable). Read-only memory), battery-backed SRAM (static RAM), and the like.
[0035]
As will be described in detail later, the reading control unit 6 performs lighting control of the light source unit 52, driving control of the sub-scanning mechanism, and analog image signal delivered from the CCD substrate 70 to A / D conversion into a digital image signal. The image data is converted and subjected to low-level image processing such as MTF correction and passed to the CPU 2.
[0036]
Specifically, the image data output unit 7 represents the image data obtained from the reading control unit 6 to a personal computer by a plotter that prints and forms on recording paper, a local area network, a predetermined serial or parallel interface, and the like. It is an interface circuit that transfers to another device. The present invention is not limited by the purpose of use of the image data obtained from the reading control unit 6.
[0037]
The operation display unit 8 is provided with various keys for accepting operation input from the user, and includes a display such as a liquid crystal display device, and displays an operation state of the device to be notified to the user and various messages. It is.
[0038]
The system bus 11 is a signal line including a data bus, an address bus, a control bus, an interrupt signal line, and the like for the above-described units to exchange data.
[0039]
FIG. 3 shows the reading control unit 6 of the image forming apparatus 1, the light source unit 82 and the CCD substrate 70 connected thereto via the harness 6a. The reading control unit 6 corresponds to a light source block individual driving unit.
[0040]
In the figure, the reading control unit 6 includes a reading control circuit 80. The reading control circuit 80 controls various operations related to document image reading. The reading control circuit 80 controls the sub-scanning mechanism 81 such as rotation control of the stepping motor and monitoring of the operation state by various sensors, while the light source unit 82 is turned on. Drive control is performed. Further, in return for supplying power and drive signals to the CCD substrate 70, an analog image signal is passed and image data obtained by performing image processing such as A / D conversion, shading correction, and MTF correction of the analog image signal. Is transferred to the CPU 2 via the system bus 9.
[0041]
The reading control circuit 80 refers to the setting information storage memory 82 for image processing. The setting contents of the setting information recording memory 82 are those stored from the CPU 2 via the system bus 9 (described later).
[0042]
The light source unit 82 includes light source blocks LED_A, LED_B, LED_C, and LED_D arranged in series in the main scanning direction.
[0043]
Each of these blocks has the same configuration, and is composed of a plurality of light emitting diode elements of the same type connected in parallel at equal intervals in the main scanning direction, and substantially has a large drive current, light emission amount, and light emission area. Equivalent to a single light emitting diode.
[0044]
Each of these blocks is connected in common to the LED power source 83 from the reading control unit 6 on the “anode” side.
[0045]
On the other hand, the “cathode” side of each block is individually connected to each driver circuit (LED_A drive Dr, etc.) on the read control unit 6 side.
[0046]
The LED_X drive Dr (X = A, B, C, or D) is controlled by a PWM signal (LED_X) from the reading control circuit 80, and when the PWM signal (LED_X) is at a high level, the output absorbs current. Drive operation.
[0047]
FIG. 4 is a diagram showing a PWM signal (LED_X) that drives each light source block LED_X (X = A, B, C, or D) constituting the light source unit 82 having the configuration shown in FIG.
[0048]
Each PWM signal is a signal synchronized with the PWM cycle, and if the PWM cycle is set sufficiently short with respect to the sub-scanning speed, it is substantially equivalent to the case where the light source unit 82 is continuously lit using a cold cathode tube or the like. The lighting effect can be obtained.
[0049]
In the present embodiment, the PWM cycle is synchronized with a period for reading one main scanning line (accumulation time of the light receiving element of the CCD 60), and the duty ratio (one accumulation time) is accurately determined in each reading main scanning line. The ratio of the time during which the light source is turned on can be set. However, if the PWM period is much shorter than the accumulation time (for example, one hundredth), synchronization between the PWM period and the main scanning line reading period is unnecessary, but high-speed switching of a large current load increases circuit cost. Therefore, it can be said that the method of this embodiment in which the PWM period and the main scanning line reading period are synchronized is preferable.
[0050]
FIG. 4 shows a case where the duty ratio of each PWM signal (LED_X) is shifted from a state where the duty ratio of each PWM signal (LED_X) is 100% (maximum output light amount) to a state where the duty ratio of each PWM signal (LED_X) is individually set. Thus, the reading control circuit 80 can individually set the duty ratio of each PWM signal (LED_X). The variable duty ratio can be set by changing the transition timing from High level to Low level during one PWM cycle, and can be easily realized by controlling the output port to be turned on / off by a software timer. This function can be easily realized by setting the duty ratio set value.
[0051]
FIG. 5 shows an example of white image data for one main scanning line (image data obtained by reading the white reference plate 51) read by illuminating the original with the light source unit 52 having the configuration shown in FIG.
[0052]
In FIG. 5, white image data for one main scanning line includes partial image data corresponding to the light source block LED_A, partial image data corresponding to the light source block LED_B, partial image data corresponding to the light source block LED_C, and light source block LED_D. It can be considered that the partial image data of the partial image data corresponding to is configured by being connected in series. Strictly speaking, the partial image data corresponding to the light source block LED_A includes light components from the light source block LED_B adjacent to the light source block LED_A, but is light far away from the block LED_A. Therefore, the impact is small.
[0053]
In the figure, the characteristic indicated by the dotted line is that at the maximum output light amount before control for adjusting the LED light amount (PWM duty ratio), which will be described later, and as described above, unevenness due to the COS4 power law of the lens 56 is obtained. This is a level corrected by a shading plate (not shown), a characteristic difference of the COS4 power law for each apparatus and a characteristic difference for each apparatus of the light source unit 52 (mutual variation in light emission amount at a duty ratio of 100% of each light source block) And since the change with time of those characteristics has not been corrected, considerable unevenness still remains.
[0054]
In the same figure, the specification indicated by the solid line is after the control for adjusting the LED light amount (PWM duty ratio), which will be described later. It can be seen that level unevenness can be corrected.
[0055]
In the image processing apparatus 1 according to the present embodiment, for each light source block LED_X (X = A, B, C, or D) constituting the light source unit 52, a duty ratio of a PWM signal (LED_X) that drives and lights them. However, if the duty ratio is different for each light source block region in the main scanning line direction, a problem may be caused depending on the content of the document.
[0056]
Specifically, as shown in FIG. 6, the document image is composed of halftone dots like a newspaper photo.
[0057]
In FIG. 6, two identical halftone dot patterns (a group of six black circles) are arranged in the main scanning direction, the left pattern is read by illumination from the light source block LED_A, and the right pattern is read from the light source block LED_B. It is read by the illumination.
[0058]
In that case, the duty ratio of the light source block LED_A (ratio of the ON (light emission) period in one accumulation time) is about 75%, and the duty ratio of the light source block LED_B is about 50%. The appearance of the black circles seen by the light receiving elements of the respective pixels constituting the CCD 60 corresponding to the positions of the black circles in the main scanning direction is considerably different. If the original image is a character or line drawing with a certain thickness or more, such a problem is unlikely to occur. However, since the halftone dot image is configured as a set of fine dots, a halftone dot image corresponding to each light source block is used. There may arise a problem that the partial image data obtained by reading the point images may have different impressions.
[0059]
Therefore, the duty ratio in each light source block may not be too small in consideration of halftone originals, and the mutual variation in duty ratio for each light source block may not be more than a certain width. It will be.
[0060]
Of the image processing, in the MTF correction, when a halftone image is read, the effect of the correction tends to be prominent, and the lighting duty ratio in each light source block is set as in this embodiment. In such a case, the smaller the light source lighting duty ratio, the larger the halftone dot beat. Therefore, when the duty ratio is small, it is desirable to take appropriate measures such as reducing the MTF correction.
[0061]
As will be described later in the present embodiment, considering that the priority is only on flattening the level of the white image signal, an adverse effect may occur when the original is a halftone original, so that an appropriate response can be made. .
[0062]
FIG. 7 shows the storage contents characteristic of the present invention in the setting information storage memory 82 included in the RAM 4, the parameter memory 5, and the reading control unit 6 of the image forming apparatus 1.
[0063]
The RAM 4 has a storage area 4a for white reference image data and a work storage area 4b for a light source block-specific information setting table.
[0064]
In the parameter memory 5, a white image signal level target range setting table is set in the storage area 5a, a duty ratio limit value setting table 5b is set in the storage area 5b, and a duty ratio / MTF correction data correspondence table is set in the storage area 5c.・ It is remembered.
[0065]
In the setting information storage memory 82, shading correction data is stored in the storage area 82a, and an information setting table for each light source block is stored in the storage area 82b. Note that the shading correction data stored in the storage area 82a is the white reference image data temporarily read in the storage area 4a when the CPU 2 reads the white reference plate 51 in the final setting state in the adjustment work described later on the side. Is set to transfer. Similarly, the table stored in the storage area 82b is set to be transferred from the storage area 4b of the RAM 4 (details will be described later).
[0066]
8A and 8B, white image data (shading correction data) stored in the storage area 4a (82a) and information setting for each light source block stored in the storage area 4b (82b), respectively. Describes the contents of the table.
[0067]
In FIG. 5A, white image data (shading correction data) includes partial image data corresponding to the light source block LED_A, partial image data corresponding to the light source block LED_B, and light source block LED_C, as already described in FIG. And the partial image data of the partial image data corresponding to the light source block LED_D are connected in series. It goes without saying that the same applies not only to white image data but also to image data obtained by reading a document image.
[0068]
In FIG. 5B, the information setting table for each light source block is configured by associating with “duty ratio” and “MTF correction data” corresponding to each light source block.
[0069]
FIG. 9 shows the contents of the white image signal level target value setting table in the storage area 5a, the duty ratio limit value setting table in the storage area 5b, and the duty ratio / MTF correction data correspondence table in the storage area 5c.
[0070]
These stored contents are referred to in a document image reading process procedure in the CPU 2 described later. In addition, since the stored contents are stored in the rewritable parameter memory 5, the setting can be changed to a more optimal value or a value according to a user's desire.
[0071]
The white image signal level target value setting table 5a indicates a range (“upper limit” and “lower limit”) in which the level of the white image signal obtained by reading the white reference plate 51 should fall.
In the figure, the “upper limit” is set to 83%, and the “lower limit” is set to 77%. In this case, 100% corresponds to the maximum input voltage that can be handled in the A / D conversion function of the reading control circuit 80. The “upper limit” can be set to 100%, but is set to “83”% because it cannot be distinguished from the case where the light source is too bright and exceeds the maximum input voltage for A / D conversion. As a result, the light amount at the duty ratio of 100% of each block constituting the light source unit 82 is not adjusted accurately so that it is always less than or equal to the maximum input voltage of A / D conversion. In addition, the light quantity can be adaptively adjusted to an optimum light amount by adjusting the duty ratio described later.
[0072]
The duty ratio limit value setting table 5b is for limiting the duty ratio set for each light source block in consideration of halftone originals, and includes a lower limit (Dmin: current setting 50%) and an upper limit difference ( ΔD: current 20%). The current setting means that the duty ratios for each light source block must all be 50% or more, and the difference between the duty ratios for each light source block must be 20% or less.
[0073]
The duty ratio / MTF correction data correspondence table shows the optimum MTF correction data (filter coefficient group) corresponding to each of the duty ratios in increments of 1% from the duty ratio of 30% to 100% (when halftone images are read). ). The MTF correction data may be calculated and generated as a function of the duty ratio.
[0074]
Next, a document image reading process procedure performed by the CPU 2 as the light amount setting unit for each light source block will be described with reference to FIGS.
[0075]
First, in FIG. 10, first, it is monitored whether there is a predetermined operation input for instructing to start reading via the operation display unit 8 (No loop of determination S101), and if there is a reading start operation (Yes of determination S101). And instructing the reading control circuit 80 via the system bus 9 to clear the shading correction data 82a (processing S102). Clearing the shading correction data 82a means that the shading correction processing in the reading control circuit 80 is set to be invalid so that uncorrected white image data can be obtained.
[0076]
Then, the scan line Ls is instructed and moved from the standby position (left side of the white reference plate 51 in FIG. 1) to the position of the white reference plate 51 (processing S103).
[0077]
Then, lighting is started by setting all the duty ratios of the respective light source blocks to 100% (processing S104). The process S104 transfers the information setting table 4b for each light source block in which the duty ratio 100% is set for all the light source blocks to the reading control circuit 80 and dummy data that is not corrected is set in the corresponding MTF correction data. And is set as the table 82b and instructed to start lighting.
[0078]
Then, the image data for one line is read by the reading control circuit 80 and acquired as white reference image data 4a.
[0079]
The acquired white reference image data corresponds to the waveform indicated by the dotted line in FIG. 5, and the signal level unevenness of each partial image data corresponding to each light source block is large. A component of microscopic variation between adjacent pixels in the sensitivity of the light receiving element is also included, and the microscopic component can be corrected only by shading correction, but other components, that is, main components in the reading optical system. Regarding components due to attenuation unevenness in the scanning direction, unevenness in the amount of light in the main scanning direction of the light source unit 82, and macroscopic unevenness in sensitivity of the light receiving element, a substantial amount of light in the main scanning direction of the light source unit 82 (one main amount). This is possible by adjusting the ratio of the lighting time in the accumulation time corresponding to the scanning line (duty ratio).
[0080]
Therefore, the average value of the signal level from each pixel (light receiving element) is calculated for each of the partial image data in the reading area corresponding to each light source block (processing S106). The variation of the average value is the variation to be corrected by adjusting the substantial light quantity in each light source block.
[0081]
Then, after calculating the optimum duty ratio for each light source block and transferring and setting the table 82b described in the table 4b, the light source unit 82 is turned on again in the reading control circuit 80 (process S107).
[0082]
  In this case, for example, when the average value in the block LED_A is 80%, the average value in the LED_B is 90%, the average value in the LED_C is 100%, and the average value in the LED_D is 95%, the duty ratio and the white image signal level (The actual relationship between the duty ratio and the white image signal level can be easily found experimentally), as shown in FIG. 9 (a). Since the target value of the white image signal level is 77% lower limit and 83% upper limit, 80% in the middleTheTarget valueWhenAnd calculate. Specifically, for LED_A, the average value is just 80%, so the duty ratio remains 100%. Since the average value of LED_B is 90%, the duty ratio is changed to 100 * 80/90 = 89%. For LED_C, the average value is 100%, so the duty ratio is changed to 100 * 80/100 = 80%. Since the average value of LED_D is 95%, it is changed to 100 * 80/95 = 84%.
[0083]
After the lighting at the estimated duty ratio is started in this way (processing S107), the process proceeds to the processing 201 in FIG. 11 to read / acquire a color reference image for one line (processing S201).
[0084]
Then, with respect to the newly acquired white reference image data, an average value is calculated for each of the partial image data corresponding to each light source block, similarly to the processing S106 of FIG. 10 (processing S202), and all the average values are calculated. If the target range (77% or more and 83% or less), the setting of the duty ratio is confirmed, so the process proceeds to step S205 (in the determination S203), but if out of the target range (in the determination S203) No), the duty ratio is finely adjusted and set only for the block outside the target range, re-lighting is started at the set duty ratio (process 204), and the process returns to process 201.
[0085]
Specifically, the fine adjustment in step S204 is performed by −1% for the block whose average value exceeds the upper limit of 83% and +1 for the block whose average value is below the lower limit of 77%. After the fine adjustment, the process S201 and the process 202 are performed again until the judgment S203 becomes Yes.
[0086]
As a result, the set duty ratio of each light source block in the table 4b when the determination in S203 is Yes is such that the average value of the white image signal level of each block falls within the target range of 77% to 83%. Thus, the level of the white image signal is flattened as shown by the solid line in FIG.
[0087]
  The processing up to this point is processing that prioritizes flattening of the signal level of white image data. However, if the original is a halftone original, as described above.InIf the duty ratio in each light source block is too small or has a difference, the image quality in the obtained image data will be affected. Therefore, the presence or absence of a light source block with a duty ratio equal to or less than Dmin shown in FIG. If there is not (No at Step S206), the process proceeds to Step S208. If there is (Yes at Step S206), the duty ratio of the corresponding block is corrected to Dmin (Step S207). .
[0088]
As a result, the duty ratio can be avoided to be equal to or less than Dmin, so that image quality deterioration at the time of halftone document reading can be avoided. In this case, however, the flatness of the signal level of the white image data is inevitably impaired to some extent, but is unavoidable.
[0089]
Further, in the processing 208, the duty ratio difference, that is, the block set to the maximum duty ratio and the duty ratio difference of the block set to the minimum duty ratio exceed the upper limit difference ΔD shown in FIG. 9B. If it does not exceed (No in S209), the process proceeds to S211. If it exceeds (Yes in S209), until ΔD or less, After the duty ratio of the block having the smallest duty ratio is increased to be equal to or smaller than ΔD (process S210), the process proceeds to process S211. However, the method of adjusting to ΔD or less is not limited thereto. For example, when ΔD is 20%, the duty ratio of the block with the maximum duty ratio is 90%, and the duty ratio of the block with the minimum duty ratio is 60%, respectively. You may make it adjust by changing to 85% and 65% and approaching each other. In the process, for example, when another block with a duty ratio of 63% appears as a block with the lowest duty ratio, the same adjustment is repeated, so that the adjustment can be made so as not to exceed ΔD.
[0090]
Thereby, it is possible to prevent image quality deterioration when the original is a halftone original. Note that the adjustment of the duty ratio in consideration of the halftone dot original document impairs the flatness of the signal level of the white image data, and therefore may not be performed for a normal character original or line drawing original. . Specifically, only when the contents of the document can be set to either “character or line drawing” or “halftone image” on the operation display unit 8 and set to “halftone image”, the process S205 is performed. Or you may make it perform process S210. As a result, the image quality of a “character or line drawing” document can be optimized.
[0091]
In process S211, the white reference plate 51 is finally read at the duty ratio (light quantity) set for each light source block to obtain white reference image data 4a (process S211), and the process proceeds to process S301 in FIG. The white reference image data 4a read at the end is set as shading correction data 82a (processing S301), and the table 4b is referred to by referring to the duty ratio / MTF correction data correspondence table shown in FIG. 9C. In step S302, MTF correction data corresponding to the duty ratio in each light source block finally set in step S102 is set. Note that this process S302 can also be performed only when “halftone image” is set, and in the case of “character or line drawing”, correction data of another pattern may be applied.
[0092]
As a result, the white reference image data is flattened as much as possible, and MTF correction with optimal correction data according to the variation in the duty ratio of the light source block is possible.
[0093]
Then, the reading control circuit 80 is instructed to start reading a document image (step S303), and image data for one main scanning line obtained from the reading control circuit 80 via the system bus 9 is stored in the RAM 4, The image data output unit 7 outputs image data (print output, transfer, etc.) while performing resolution conversion or encoding / compression processing (processing S306).
[0094]
The process S306 is continued until the reading of one page of the original is completed (No loop in the determination S305). When the reading is completed (Yes in the determination S305), the light source unit 82 is turned off (the PWM signal for each light source block). The scan line Ls is returned to the standby position (process 307), and the process S is terminated.
[0095]
Note that, in the reading in step S304, if the image forming apparatus 1 includes an automatic document feeder, a plurality of pages of documents may be continuously read.
[0096]
Further, in the reading of the process S304, the reading control circuit 80 A / D changes the image signal obtained from the CCD substrate 70 in units of one main scanning line, and performs the shading with reference to the shading correction data 82a set in the process S301. Further, MTF correction is performed with reference to the information setting table 82b for each light source block. In the MTF correction in that case, the MTF correction data set in the table 82b is switched and referenced for each of the partial image data in the main scanning direction corresponding to each light source block of LED_A to LED_D, and the duty ratio adaptive image correction means The image correction process is performed.
[0097]
FIG. 13 shows a modification of the arrangement configuration of each light source block in the light source unit 82 shown in FIG.
[0098]
In FIG. 13, one of the differences from FIG. 3 is that a light source unit 82 is configured by serial arrangement of five light source blocks of LED_A to LED_E in the main scanning direction.
[0099]
However, it is not an essential difference, and the biggest difference is that the “cathode” sides of the LED_B and D adjacent to the central LED_C are connected to each other and connected to a common LED_BD drive Dr. Further, the “cathode” sides of the LED_A and E at both ends are connected to each other and connected to a common LED_AE drive Dr.
[0100]
As described above, physically, the five light source blocks LED_A to E are connected in series in the main scanning direction, but electrically, only the three light source blocks LED_C, LED_AE, and LED_BD are configured. become.
[0101]
Thereby, the number of harnesses 6a can be reduced, and the number of driving Dr circuits can be reduced.
[0102]
In that case, the light amount (duty ratio) of the two light source blocks LED_A and LED_E is controlled by a single PWM signal (LED_AE), and the light amount (duty ratio) of the two light source blocks LED_B and LED_D is simply It is controlled by one PWM signal (LED_BD), and the duty ratio cannot be set independently as shown in FIG.
[0103]
However, the signal level of the white image data can still be sufficiently flattened. In the image processing apparatus 1 according to this embodiment using a CCD as a line image sensor, unevenness in the signal level of the white image data in the main scanning direction is mainly caused by the lens 56 on the left and right objects according to the COS4 power law. This is because the component due to the difference in the degree of attenuation of transmitted light in the scanning direction is dominant as shown by the dashed line waveform in FIG.
[0104]
In other words, the difference in the degree of attenuation of transmitted light generated in the left and right objects in the main scanning direction due to the COS4 law is different from the sensitivity variation of each light receiving element in the CCD 60 which differs from device to device. Since the occurrence and the tendency of the occurrence are known, it is possible to cancel in advance by making the maximum output light amount of each light source block when the duty ratio is 100% uneven.
[0105]
Specifically, as schematically shown in FIG. 15, not only the light source blocks LED_A to LED_E are arranged in series in the main scanning direction, but also the arrangement density of the light emitting diode elements constituting each block is attenuated by the COS4 power law. LED_C, which is responsible for the central part with a small amount of light, is low, LED_A and LED_E that light both ends with high attenuation are high, and the intermediate LED_B and LED_D are non-uniformly arranged, such as a medium density To do.
[0106]
If the light emitting diodes constituting each block are driven at a maximum rating (for example, a current of 30 mA) at a duty ratio of 100%, the number of arrangements per unit area corresponds to the density of light emission. By changing the drive current at a duty ratio of 100%, it is possible to change the density of the light emission amount in the main scanning direction, but the number of necessary light emitting diode elements increases accordingly.
[0107]
Note that, in a specific light source block, for example, LED_E, the light emitting diode elements may not be arranged uniformly in the main scanning direction, but may be arranged so that the arrangement density increases toward the end. In that case, the white image signal level unevenness due to the COS4 power law factor can be corrected more finely.
[0108]
The adjustment of the arrangement density of the light emitting diode elements constituting the light source block in the main scanning direction not only corrects the unevenness of the left and right objects in the main scanning direction but also corrects the unevenness of the asymmetrical but predictable property in the main scanning direction. Needless to say, this is effective. However, in that case, it is necessary to drive each light source block individually.
[0109]
Further, by modifying the arrangement density of the light-emitting diode elements in each light source block as described above, it is possible to correct the unevenness of the white image signal level due to the COS4 power law factor as shown by the waveform shown by the dotted line in FIG. Correction is not necessary, and the size and cost of the apparatus can be reduced accordingly.
[0110]
Further, by performing the document reading processing procedure of FIGS. 10 to 12 with the configuration of FIGS. 14 and 15, adaptive light quantity (duty ratio) adjustment for each light source block is performed, and the waveform shown by the solid line in FIG. As can be seen, it is clear that the signal level of the white image data can be further flattened. In that case, however, the duty ratio adjustment target is changed from four LED_A to LED_D to three LED_C, LED_AE, and LED_BD. Control is simplified by reducing the number of light source blocks as seen from the adjustment of the duty ratio.
[0111]
Also, common MTF correction data is applied to LED_A and LED_E, or LED_B and LED_D, respectively, while they are arranged apart from each other in the main scanning direction. It is necessary to consider points.
[0112]
  In the embodiment described above, each light source block is constituted by a parallel position of a large number of light emitting diode elements. However, each light source block may be constituted by, for example, a surface light emitting element, and the light emission of each light source block. The amount may be adjusted not by the duty ratio of the drive signal but by linear increase or decrease of the supply voltage or current.
  According to the image reading apparatus as described above, the distribution in the main scanning direction of the amount of light emitted from the light source to the scan line on the reading surface of the document from the light source is in the main scanning direction of the white image data. Since the signal level is adaptively controlled so as to be flat, the density unevenness of the image can be almost eliminated without shading correction in the subsequent image processing, and even when shading correction is performed in the subsequent image processing, the image information Since the omission can be minimized, an effect that the image quality of the obtained image data can be improved is obtained. Further, since the light emission amount in each light source block is automatically adjusted to a necessary and sufficient amount, it is possible to minimize power consumption and heat generation required for document illumination.
Further, if the known attenuation characteristics in the reading optical system are canceled out, the adjustment amount of the light amount of each light source block is not wasted. Therefore, the light amount in each light source block can be effectively utilized. An effect that adjustment can be performed with a margin is obtained. Further, if the known attenuation characteristic in the reading optical system is canceled by setting the maximum output light amount of each light source block, a physical additive such as a shading plate for canceling the attenuation characteristic becomes unnecessary. Therefore, the space can be reduced accordingly.
When a reduction optical system including a lens is used as the line image sensor and a lens is used as the reading optical system, the amount of attenuation increases symmetrically toward the left and right ends in the main scanning direction according to the COS4 law of the lens. In addition, if two light source blocks located almost symmetrically are driven as one light source block, the drive circuit and wiring can be simplified, and correction by a physical additive such as a shading plate is unnecessary. Therefore, the space can be reduced accordingly.
Further, if each of the light source blocks is configured by a parallel arrangement of light emitting diode elements that consumes less power than the amount of output light, it is possible to further reduce heat generation and power consumption associated with document illumination.
If the light quantity of each light source block can be individually set by so-called PWM control that changes the duty ratio, the light quantity can be adjusted without extra heat generation.
In view of the possibility that the content of the document may be a halftone dot image, an image obtained by reading a halftone dot image if no light source block has a duty ratio equal to or lower than a predetermined lower limit value. The change in the beat of the halftone dot output in the main scanning direction due to the difference in the set duty ratio in each light source block in the data can be restricted, and image quality deterioration can be prevented.
Further, in view of the possibility that the content of the document may be a halftone image, if the difference in the set value of the duty ratio in each light source block is greater than a predetermined upper limit difference, The difference in halftone dot beats in the main scanning direction due to the difference in the set duty ratio in each light source block in the image data obtained by reading the halftone image can be limited to a certain level or less, thereby preventing image quality deterioration. It becomes possible.
Further, when image processing such as MTF correction processing S is performed on the obtained image data, each partial image data read by illumination with a light source that is lighted and driven with a duty ratio set for each light source block. If an optimum correction is made to the duty ratio, it is possible to prevent image quality deterioration caused by different lighting drive duty ratios in the respective light source blocks in the main scanning direction and to maintain high image quality.
[0113]
【The invention's effect】
  According to the image reading apparatus of the present invention described above, a document image can be read with uniform sensitivity in the main scanning direction, power consumption and heat generation required for document illumination can be minimized, and document Therefore, it is possible to prevent deterioration of the image quality when the image is a halftone document and to maintain high image quality.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing a scanner mechanism of an image processing apparatus according to an embodiment of the present invention.
FIG. 2 is a block diagram illustrating an image forming apparatus according to an embodiment of the present invention.
FIG. 3 is a diagram illustrating a reading control unit, a light source unit connected to the reading control unit via a harness, a CCD substrate, and the like in the image forming apparatus according to the embodiment of the present invention.
4 is a diagram showing a PWM signal for driving and lighting each light source block constituting the light source unit having the configuration shown in FIG. 3; FIG.
5 is a diagram showing an example of signal levels of white reference image data obtained by reading reflected light applied to a white reference plate from the light source unit having the configuration shown in FIG. 3;
FIG. 6 is a diagram for explaining a difference in reading method due to a difference in duty ratio of a light source lighting drive when a halftone document is read.
FIG. 7 is a diagram showing storage contents of a RAM, a parameter memory, and a setting information storage memory of the image forming apparatus according to the embodiment of the present invention.
FIG. 8 is a diagram illustrating the contents of white image data (shading correction data) and an information setting table for each light source block.
FIG. 9 is a diagram showing the contents of a white image signal level target value setting table, a duty ratio limit value setting table, and a duty ratio / MTF correction data correspondence table.
FIG. 10 is a flowchart showing a document image reading processing procedure in the image forming apparatus according to the embodiment of the present invention.
11 is a flowchart showing a document image reading processing procedure in the image forming apparatus according to the embodiment of the present invention, together with FIG. 10;
12 is a flowchart showing a document image reading processing procedure in the image forming apparatus according to the embodiment of the present invention, together with FIGS. 10 and 11. FIG.
13 is a modification of the configuration of FIG. 3 showing the reading control unit, the light source unit connected to the reading control unit via a harness, the CCD substrate, and the like of the image forming apparatus according to the embodiment of the present invention.
14 is a diagram showing a PWM signal for driving each light source block constituting the light source unit having the configuration shown in FIG.
15 is a diagram showing an example of signal levels of white reference image data obtained by reading reflected light irradiated on a white reference plate from the light source unit having the configuration shown in FIG.
[Explanation of symbols]
1 Image forming device
6 Reading control unit
52 Light source unit
60 CCD

Claims (5)

A light source for moving the scan line in the main scanning direction, which is the current reading position on the reading surface of the document, in the sub-scanning direction, and illuminating the scan line on the reading surface over the entire main scanning direction; In an image reading apparatus that obtains image data corresponding to the reading surface of the original by photoelectrically converting light reflected from the scan line on the reading surface by a line image sensor,
While configuring the light source as a plurality of light source blocks arranged in the main scanning direction,
Light source block individual driving means for driving and lighting with a set light amount that is equal to or less than the maximum output light amount for each of the light source blocks,
Prior to the start of document reading, each of the light source blocks is supplied to the individual light source block driving means so that the signal level in the main scanning direction of white image data obtained by reading the white reference plate with the line image sensor becomes substantially constant. Light amount setting means for each light source block that adaptively sets the light amount of
The setting and driving of the light amount of each light source block is performed by changing a duty ratio which is a ratio of a light emission period in a predetermined driving cycle,
When reading a halftone document, the light amount setting means for each light source block is configured so that the signal level in the main scanning direction of white image data obtained by reading the white reference plate with the line image sensor is substantially constant. When the light amount of the light source block is adaptively set by setting the duty ratio, if the set value of the duty ratio falls below a predetermined lower limit value, the setting to the lower limit duty ratio is not performed, and further, When the difference between the maximum value and the minimum value of the duty ratio setting value for each light source block exceeds a predetermined upper limit difference, the difference in the duty ratio setting value for each light source block is An image reading apparatus , wherein a duty ratio for each of the light source blocks is set within a range equal to or less than the upper limit difference .   The maximum output light amount for each of the light source blocks constituting the light source is a known attenuation in the main scanning direction in the reading optical system through which reflected light from the scan line of the document passes before entering the image sensor. The image reading apparatus according to claim 1, wherein the image reading apparatus is set to an amount that substantially cancels characteristics. The maximum output light amount for each of the light source blocks constituting the light source is substantially bilaterally symmetrical in the main scanning direction of the reading optical system through which reflected light from the scan line of the document passes before entering the image sensor. While this is set to an amount that almost cancels the known attenuation characteristics,
2. The light source block individual drive means drives two light source blocks that are substantially symmetrical in the main scanning direction among the light source blocks as one light source block. Image reading apparatus.   4. The image reading apparatus according to claim 1, wherein each of the light source blocks is configured by a parallel arrangement of a plurality of light emitting diode elements in the main scanning direction. When performing a predetermined image correction process on the document image data obtained from the line image sensor, for each of the partial image data corresponding to each of the light source blocks in the main scanning direction, 2. The image reading apparatus according to claim 1, further comprising duty ratio adaptive image correction means for performing correction suitable for each duty ratio set by the light source block-specific light amount setting means.

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